📚 Common Mistakes in IB & CIE Biology Exam Questions | IB 与 CIE 生物易错题精讲
In both IB and CIE biology exams, certain concepts consistently trip up students due to subtle distinctions or widespread misconceptions. This article dissects 10 of the most common pitfalls, providing clear explanations and contrasting the correct ideas with typical errors. By analysing these tricky questions, you will sharpen your understanding and avoid losing easy marks.
在IB和CIE生物考试中，某些概念因细微差别或普遍误解而反复让学生出错。本文剖析10个最常见的陷阱，提供清晰的解释，并将正确观点与典型错误进行对比。通过分析这些易错题，你将加深理解，避免丢分。
1. Cell Respiration vs. Gas Exchange | 细胞呼吸与气体交换
Mistake 1: Students often write that ‘breathing provides oxygen for respiration’ as if they are the same process. In fact, breathing (ventilation) is the physical movement of air in and out of the lungs; gas exchange is the diffusion of O₂ and CO₂ across the alveolar and capillary walls; cellular respiration is the biochemical release of energy from organic molecules inside cells. Examiners expect you to distinguish these terms precisely.
错误1：学生常写“呼吸为细胞呼吸提供氧气”，好像它们是同一过程。实际上，呼吸（通气）是空气进出肺的物理运动；气体交换是O₂和CO₂通过肺泡和毛细血管壁的扩散；细胞呼吸是细胞内有机物释放能量的生化过程。考官希望你准确区分这些术语。
Mistake 2: Another common error is stating that respiration occurs in the lungs. Aerobic respiration actually takes place in the mitochondria of cells throughout the body. The lungs merely supply oxygen and remove carbon dioxide. In essays, always specify the site: cytoplasm (glycolysis) and mitochondrial matrix / cristae (Krebs cycle & electron transport chain).
错误2：另一个常见错误是声称呼吸作用发生在肺部。有氧呼吸实际发生在全身细胞的线粒体中。肺只负责供氧和排出二氧化碳。在论述题中，务必注明场所：细胞质（糖酵解）和线粒体基质/嵴（克雷布斯循环和电子传递链）。
2. Photosynthesis: Light-Dependent vs. Light-Independent Reactions | 光合作用：光反应与暗反应
Mistake 1: Calling the Calvin cycle the ‘dark reaction’ is misleading and often penalised. The Calvin cycle does not directly require light, but it depends on ATP and NADPH produced in the light-dependent reactions. In CIE and IB, it is correctly referred to as the light-independent stage, and it occurs in the stroma, not requiring darkness.
错误1：把卡尔文循环称作“暗反应”具有误导性，常被扣分。卡尔文循环不直接需要光，但依赖于光反应产生的ATP和NADPH。在CIE和IB中，应正确称呼其为光不依赖阶段，它在基质中进行，不需要黑暗。
Mistake 2: Many students confuse the products of the light-dependent reactions (ATP, NADPH, O₂) with those of the Calvin cycle (G3P, which leads to glucose, ADP, NADP⁺). Remember that photolysis of water produces O₂ and electrons, and the oxygen released comes from water, not CO₂.
错误2：许多学生混淆光反应产物（ATP、NADPH、O₂）与卡尔文循环产物（G3P，进而生成葡萄糖，以及ADP、NADP⁺）。记住水的光解产生O₂和电子，释放的氧气来自水，而非CO₂。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
3. Mitosis and Meiosis: Chromosome Number Changes | 有丝分裂与减数分裂中染色体数目变化
Mistake 1: A frequent error is believing that mitosis halves the chromosome number. In mitosis, a diploid parent cell produces two genetically identical diploid daughter cells. Meiosis, on the other hand, halves the chromosome number to produce haploid gametes. In exams, pay attention to whether the question asks about chromosome number or DNA mass – they change differently.
错误1：常见错误是认为有丝分裂使染色体数目减半。有丝分裂中，二倍体亲代细胞产生两个遗传相同的二倍体子细胞。而减数分裂将染色体数目减半，产生单倍体配子。考试中注意问题是问染色体数目还是DNA质量——它们变化不同。
Mistake 2: Confusing ‘homologous chromosomes’ and ‘sister chromatids’ leads to marks lost in diagram questions. Homologous chromosomes pair up during meiosis I, but sister chromatids are separated during meiosis II and mitosis. When labelling, identify clearly if the structure is a chromosome (two sister chromatids joined at the centromere) or a single chromatid.
错误2：混淆“同源染色体”和“姐妹染色单体”导致在图像题中丢分。同源染色体在减数第一次分裂时配对，而姐妹染色单体在减数第二次分裂和有丝分裂中分离。标注时，要明确结构是染色体（由两个姐妹染色单体在着丝粒处相连）还是单个染色单体。
4. Genetic Pedigree Analysis: Dominant vs. Recessive | 遗传系谱分析：显性与隐性
Mistake 1: Students often assume a trait is dominant just because it appears in every generation. While dominant traits typically appear in each generation, autosomal recessive traits can also skip generations. The key clue for autosomal recessive is that two unaffected parents can have an affected child. If a trait is dominant, every affected individual has at least one affected parent.
错误1：学生常因某性状在每代都出现而假定它为显性。虽然显性性状通常每代出现，常染色体隐性性状也可隔代出现。常染色体隐性的关键线索是两个正常父母能生出患病孩子。若是显性，每个患者至少有一个患病的亲代。
Mistake 2: In X-linked recessive pedigrees, mothers are carriers and more males are affected. A common pitfall is forgetting that an affected father cannot pass the X-linked allele to his son (since he passes his Y chromosome). Thus, all daughters of an affected male are carriers (or affected if the condition is dominant). Always check the sex distribution.
错误2：在X连锁隐性系谱中，母亲是携带者，更多男性患病。常见陷阱是忘记患病父亲不能将X连锁等位基因传给儿子（因为他传递Y染色体）。因此，患病男性的所有女儿都是携带者（如果疾病为显性则患病）。务必检查性别分布。
5. Natural Selection vs. Genetic Drift | 自然选择与遗传漂变
Mistake 1: Students sometimes describe any change in allele frequency as natural selection. However, genetic drift is a random change in allele frequencies due to chance events, especially in small populations. Selection is non-random and driven by differential survival and reproduction. In IB and CIE questions, you must mention ‘selection pressure’ and ‘differential reproductive success’ for natural selection.
错误1：学生有时把任何等位基因频率的改变都描述为自然选择。然而，遗传漂变是因偶然事件引起的随机等位基因频率变化，尤其是在小种群中。选择是非随机的，由差异生存和繁殖驱动。在IB和CIE考题中，必须提到“选择压力”和“差异繁殖成功”来解释自然选择。
Mistake 2: Another error is stating that antibiotic resistance arises because bacteria ‘learn’ to tolerate the drug. The correct mechanism: pre-existing genetic variation means some bacteria already possess resistance genes; antibiotics act as a selection pressure, killing susceptible bacteria and leaving resistant ones to reproduce. This is a classic example of directional selection.
错误2：另一错误是声称抗生素耐药性的产生是因为细菌“学会”了耐受药物。正确机制：预先存在的遗传变异意味着某些细菌已拥有耐药基因；抗生素作为选择压力，杀死敏感细菌，留下耐药菌繁殖。这是定向选择的经典例子。
6. Nephron: Ultrafiltration vs. Selective Reabsorption | 肾单位：超滤与重吸收
Mistake 1: Confusing the location of ultrafiltration. Many answers wrongly place it in the Bowman’s capsule alone. Ultrafiltration occurs from the glomerulus into the Bowman’s capsule, driven by high hydrostatic pressure. The filtrate contains water, glucose, ions, and urea but no large proteins or cells. Examiners expect you to mention the basement membrane and fenestrated capillaries.
错误1：混淆超滤的场所。许多答案错误地将其仅放在鲍曼囊。超滤是从肾小球进入鲍曼囊，由高静水压驱动。滤液包含水、葡萄糖、离子和尿素，但无大分子蛋白质或细胞。考官希望你提到基膜和有孔毛细血管。
Mistake 2: Students often say that all glucose is reabsorbed in the proximal convoluted tubule, but they forget to include that reabsorption is by active transport and facilitated diffusion. Also, water reabsorption in the collecting duct is regulated by ADH, increasing permeability. Failing to link osmosis and ADH leads to lost marks in homeostasis questions.
错误2：学生常说所有葡萄糖在近曲小管被重吸收，但忘记说明重吸收通过主动转运和易化扩散进行。此外，集合管对水的重吸收受抗利尿激素(ADH)调控，增加通透性。未能将渗透与ADH联系起来，会在稳态题中丢分。
7. Synaptic Transmission and Action Potential Propagation | 突触传递与动作电位传导
Mistake 1: Describing the action potential as ‘jumping’ from one node to the next can be too vague. Saltatory conduction is the propagation of action potentials along myelinated axons, where depolarisation only occurs at nodes of Ranvier. This increases speed. Always explain that myelin prevents ion leakage and that the local circuits set up depolarisation at the next node.
错误1：将动作电位描述为从一个节点“跳跃”到下一个节点可能太模糊。跳跃传导是动作电位沿有髓轴突传播，去极化仅发生在郎飞氏结处，从而加快速度。一定要解释髓鞘阻止离子泄漏，局部回路在下一个结处引起去极化。
Mistake 2: In the synapse, many students write that the neurotransmitter enters the postsynaptic neurone. In fact, it binds to receptors, causing ion channels to open (e.g. Na⁺ channels) leading to an excitatory postsynaptic potential. Neurotransmitter is then broken down or reabsorbed, not entering the cell. Confusing the direction of ion flow (e.g. Ca²⁺ influx in the presynaptic knob) is another common slip.
错误2：在突触中，许多学生写神经递质进入突触后神经元。实际上，它与受体结合，引起离子通道打开（如Na⁺通道），产生兴奋性突触后电位。神经递质随后被分解或重吸收，而不进入细胞。混淆离子流动方向（如突触前小结Ca²⁺内流）是另一常见疏忽。
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